The patch on bug 1837570 that moves most playback mirrors to canonical-initated connections is now causing permoranges after having been green in the past.

The changes to dom/media that landed since that green try run, and that could affect this seem to be bug 1829054 and bug 1835804. I'll try to verify which one it was.

This is a followup to try and get the permorance-causing patch landed, while not blocking the others.

This shortens the time it takes to establish the connections for canonicals
living on the main thread, from the thread hop chain:
main thread (MediaDecoderStateMachine::Init)
-> state machine task queue (Mirror::Connect)
-> main thread (AbstractCanonical::AddMirror)
-> state machine task queue (AbstractMirror::UpdateValue)

to the thread hop chain:
main thread (MediaDecoderStateMachine::Init + Canonical::ConnectMirror)
-> state machine task queue (Mirror::AbstractUpdateValue)

No races exist here as MediaDecoderStateMachine initiates its shutdown on main
thread and continues on the task queue (where the mirrors live).

Found the problem: https://phabricator.services.mozilla.com/D181811
This can land once that has made it to autoland then.

https://hg.mozilla.org/mozilla-central/rev/1dd0fcd5e1cf